You Are Here: Home > About Arthritis > Arthritis Types (A - Z) > Myositis (dermatomyositis, polymyositis)

Myositis (dermatomyositis, polymyositis)

Myositis is a type of autoimmune disease in which the body’s immune system (which is supposed to fight off infection) becomes confused and starts attacking normal muscle causing damage and inflammation (myo = muscle, itis = inflammation). While muscle inflammation is the primary characteristic of this form of arthritis, myositis can also affect a number of organs such as your skin, lungs or heart. Myositis belongs to a larger group of diseases called myopathies, which are diseases that affect your muscles.

Until recently, myositis was divided into two types: dermatomyositis (myositis with a skin rash) and polymyositis (myositis without a skin rash). Other forms of myositis have since been recognized, such as immune-mediated necrotizing myopathy, overlap myositis (myositis associated with the presence of another connective-tissue disease, such as systemic sclerosis or lupus), and inclusion-body myositis.

Myositis typically affects the large muscles of the arms and legs on both sides of the body, but can also affect muscles associated with swallowing or breathing, and in rare cases can affect the heart as well.

With treatment, patients can achieve periods of no active symptoms (remission), but the disease tends to recur with periods of active symptoms (flare).

Myositis can occur alone or in combination with another autoimmune disease such as rheumatoid arthritis, lupus or scleroderma (overlap myositis). In some patients, scarring of the lungs called pulmonary fibrosis can occur.


What are early signs of myositis?

Muscle Weakness: Usually, the main symptom of myositis is muscle weakness. At the onset of the disease it generally affects the thighs and hips. If you have myositis, you may have difficulty climbing stairs or rising from low surfaces. The distance you are able to walk may eventually be limited because your muscles get too tired.

If your shoulders are involved, you may have trouble getting dressed, combing your hair or lifting heavy objects. If myositis affects your neck, chest and abdomen muscles it may be hard to lift your head from a pillow or get out of bed. Polymyositis can also cause you to have trouble swallowing or talking, though these are less common results of the disease. In inclusion-body myositis, the muscle weakness usually affects one side of the body (asymmetrical), and involves muscles on the back of the arm and hand that extend the fingers.

Your muscles may feel a bit sore and tender. Muscle pain is not a major feature of these diseases. If you’re very sore a different disease may need to be considered.

Skin Rash: Dermatomyositis is a myositis associated with the presence of a specific skin rash. This skin rash may precede, accompany or follow muscle weakness. It is usually found on sun-exposed areas such as the face (eyelids, cheeks), scalp, neck, chest and hands (over knuckles, around nails). It can also appear on the elbows, knees, ankles, upper arms and thighs. This type of rash is often deep red in color (almost purple) and may be slightly raised. The rash lasts for weeks without treatment and may be difficult to treat in some people.

Joint Pain: Inflammatory joint pain and/or swelling may precede or accompany muscle weakness. It usually affects small (ex: hands) and medium (ex: wrist) joints in a symmetric fashion similar to rheumatoid arthritis (RA), however myositis is generally considered less aggressive than RA in terms of joint damage and risk of deformity.

Lung Involvement: Myositis can cause weakness of the muscles required for breathing, resulting in coughing and shortness of breath. It may also cause fibrosis (build-up of scar tissue) in the lungs. In some individuals, the inflammatory process can affect the lung tissue resulting in a condition called interstitial lung disease.

Heart Involvement: In rare cases myositis can cause inflammation of the heart muscle (myocarditis), resulting in poor heart function (called congestive heart failure). It can also lead to water retention, shortness of breath and leg swelling.

Calcium Deposits: The skin and muscles can become hardened due to an accumulation of calcium salt deposits. This process, called calcification, doesn't often occur in adults with the disease, but children with dermatomyositis may develop calcium deposits years after the disease starts. The deposits generally develop in the shoulder, pelvis, hip, calf and thigh and may severely limit motion. The masses that develop under the skin can rupture and the calcium salts may drain.

How is myositis diagnosed?

To be able to diagnose whether you have myositis, your doctor will perform a physical examination revealing muscle weakness, skin rash, joint pain and/or swelling or breathing difficulties.

The next step will be to order a series of tests, as there are many other causes of muscle weakness to rule out. These tests include:

  • Muscle enzymes: Different substances can be measured in the blood, and are found in increased levels following muscle damage. Creatine kinase (CK) is one common enzyme test, but there are others. Of note, these markers are not specific for myositis and can be elevated for other reasons.
  • Autoantibodies: The presence of autoimmune markers in the blood can support a myositis diagnosis. Autoantibodies, found in over 50% of myositis subjects, predict organ involvement pattern (heart, lungs, joints), response to treatment and outcome.
  • Electromyogram (EMG); muscle magnetic resonance imaging (MRI): These tests may be performed to confirm presence of muscle disease and help select a muscle biopsy site. An EMG measures electric activity in muscles and nerves using electrodes taped on your skin. An MRI is somewhat like an X-ray in that it creates a picture of the inside of your body, but where X-rays are only used for seeing bones, an MRI can take a picture of your muscles using magnetic fields instead of radiation. (Note that while an MRI is a safe procedure, it should not be performed if you have a pacemaker or specific metallic implants.)
  • Muscle biopsy: Obtaining a muscle tissue sample is an important step for confirming a myositis diagnosis. Under local anesthesia, a very small piece of muscle will be surgically removed, usually in the shoulder or thigh, and examined under a microscope.

Additional tests or imaging may be used to check for heart or lung involvement, such as an electrocardiogram (ECG), cardiac ultrasound and/or MRI, pulmonary function tests or thoracic CT-scan.

Often your doctor will not be able to complete these various tests in a single visit: it might require a few trips to the hospital. However, they are important to confirm your diagnosis and plan your treatment.

What are the risk factors for myositis?

Myositis is an autoimmune disease. This means that it begins with the immune system (which normally protects the body from germs, viruses, and bacteria) malfunctioning. The immune system generates antibodies that attack healthy tissues in other parts of the body – in this case, in the muscles – causing inflammation and weakness. No one knows why the immune system does this, but it may involve a combination of environmental factors (such as viral infections, certain medications, smoking) and genetic factors (a tendency to develop the disease based on the presence or absence of particular genes). It is not an inherited disease: patients do not transmit the disease to their children.

How common is myositis?

Myositis is a rare disease. Even though this condition can occur at any age (including among children), it most commonly affects middle-aged adults. Overall, one to five new cases of myositis per 100,000 persons are seen every year. Women are usually more affected than men, however inclusion-body myositis is more common in men over 50.


Myositis is a treatable disease using medications and rehabilitation. Drug treatment is used to block inflammation and regulate the immune system. Most individuals respond well to treatment, except for inclusion-body myositis (IBM) which appears to be refractory to standard therapy. Clinical trials are underway to find effective treatments for IBM.

Some people only have a single attack of the disease and are able to stop taking medications after a few years. Other may experience chronic recurrence of the disease, requiring a long-term treatment. These individuals are often given regular low doses of medication to achieve remission. When the disease is under control, active physical therapy to help reduce inflammation and rebuild muscle strength can improve the patient’s outcome. Side effects of medications must be carefully monitored through regular blood tests, watching for signs of infection (such as pneumonia), vaccination and osteoporosis prevention.

In adults, dermatomyositis may be occasionally associated with the presence of cancer, especially within three years of diagnosis. At diagnosis, a cancer screening is performed (even in the absence of other symptoms), and cancer risk is thereafter assessed annually. Early diagnosis of cancer and prompt treatment is mandatory. This risk is only reported in adults – it is not seen in children.

For a person diagnosed with myositis, the rheumatologist is the leader of your health-care team


Prednisone (a form of cortisone) is the main treatment for both dermatomyositis and polymyositis. Prednisone is a very effective medication, but it has lots of side effects. Most people will also be treated with other medications to allow for a smaller overall dose of prednisone. Common medications used for both diseases include methotrexate and azathioprine. Hydroxychloroquine may be used for the skin rash of dermatomyositis. In severe cases, a blood product called immunoglobulin (called IVIG) is given intravenously (through a line into the bloodstream) to control inflammation.

Arthritis medications are designed to control disease, slow its progression, and to help manage pain. There is a wide range of options – with new ones coming on the horizon – so understanding all possible treatments is not easy.

These medications can be very complex, so you are encouraged to ask for in-depth explanations from your health care team – including pharmacists, who are an excellent source of information.

To explore this area of treatment, the Arthritis Society has developed a comprehensive expert guide that delivers detailed information on medications used to treat arthritis.

EXPLORE: Arthritis Medications – A Reference Guide

The optimal treatment is what is best in each individual case – so speak with your doctor and/or pharmacist about what kind of medications are most appropriate for you.


In addition to following your treatment plan, there is a lot you can do yourself to help decrease your pain and increase your movement. Physiotherapy, occupational therapy, regular exercise and relaxation techniques are very important parts of your overall treatment plan. Although you can undertake many of these activities on your own, it is important to assemble a health-care team who can help oversee and direct your self-management efforts. Learning as much as you can about the disease is also important to help you make informed decisions about treatment and lifestyle, and maximize your quality of life.


Only gentle exercise is generally recommended during periods of very active disease. Strength training should be done when symptoms are under control to keep muscles from becoming too weak and to rebuild your strength. Always consult your doctor before beginning an exercise program. He or she may also be able to refer you to a physical therapist who can advise you of the forms of exercise that are likely to be helpful, and those that could be harmful. If the disease has impaired your breathing, your therapist can instruct you in breathing exercises.


Prednisone can make people feel very hungry and gain large amounts of weight. Watching your diet and eating well while on prednisone is very important. Prednisone can also rob your bones of calcium and cause osteoporosis. A combination of diet and supplements may be necessary to ensure you are getting sufficient calcium (1200 mg/day) and Vitamin D (1000 IU/day).


Many of the medications used to treat these diseases can have side effects. It’s important to keep your doctor informed if these are happening, or if you feel your disease is getting worse.

Heat & Cold

Taking a warm shower and using warm packs are great ways to help reduce muscle pain and stiffness. Always use a protective barrier, such as a towel, between the warm pack and the skin. Heat is ideal for:

  • Relieving pain
  • Relieving muscle spasms and tightness
  • Enhancing range of motion

IMPORTANT: Do not use heat on an already inflamed muscle, as it can make symptoms worse.

Using a commercial cold pack or a homemade one (from crushed ice, ice cubes or a bag of frozen vegetables) can be helpful to help provide short-term relief from inflammation. Always use a protective barrier, such as a towel, between the cold pack and the skin. Cold is ideal for:

  • Swelling
  • Decreasing pain
  • Constricting blood flow to an inflamed muscle

For more information about using heat or cold, visit our Pain Management page.

Relaxation and coping skills

Developing good relaxation and coping skills can help you maintain balance in your life, giving you a greater feeling of control over your arthritis and a more positive outlook. Relaxation can help ease tense or inflamed muscles and reduce pain. There are many ways to relax. Try deep breathing exercises. Listen to music or relaxation tapes. Imagine or visualize a pleasant and restful activity, such as lying on a beach.

For more information about relaxation and coping skills, visit our Pain Management page. 

What Now

Living well with arthritis

There is a lot you can do to take control and actively manage your arthritis. Below we have listed a few resources to help you learn more about actively managing your arthritis to live better.


To find health & wellness advice, self-management tips, inspirational stories, and much more.

Explore Flourish

Online Learning

Our online courses are jam-packed with helpful tips and information.  Each course is devoted to a specific issue or symptom linked to arthritis.

Discover Arthritis Courses

Workshops and Webinars

Learn about upcoming educational events and webinars.

Find Workshops and Webinars

Navigating Through Arthritis

Learn about information and services available.

Navigate through arthritis


This information was last updated September 2017, with expert advice from:

Océane Landon-Cardinal, MD
Division of Rheumatology, Department of Medicine
Centre Hospitalier de l'Université de Montréal

Valérie Leclair, MD
Division of Rheumatology, Department of Medicine
Jewish General Hospital
Montréal, Québec, Canada

David Robinson, MD
Associate Professor, Internal Medicine
University of Manitoba Faculty of Medicine

Ophir Vinik, MD
Staff Physician, Department of Medicine – St. Michael’s Hospital
Associate Professor, Faculty of Medicine – University of Toronto

View All Arthritis Types (A - Z)